Hageman factor or blood coagulation factor XII is a mammalian plasma protein which, in man, is concerned with activation of blood clotting, kinin generation, and fibrinolysis. These pathways interact with the complement pathway to form an interdependent system involved in inflammation and other host defense mechanisms. Deficiency of this factor is termed Hageman trait and has been described in several hundred people. Much of the knowledge concerning Hageman factor dependent pathways has been obtained from in vitro studies utilizing Hageman trait and normal control plasma. Direct extrapolation cannot be made from these in vitro studies to the in vivo situation. An animal model with a selective, hereditary deficiency of factor XII would, therefore, be very useful in studies designed to elucidate how Hageman factor dependent pathways function in vivo as well as in vitro. A potential model of Hageman trait is a small colony of cats which was discovered and is being established at the University of Missouri. The present proposal describes investigations designed to define the nature of Hageman trait in cats in relation to its genetic, antigenic, and hematologic characteristics and its potential as a model for endotoxin induced DIC. Procedures and techniques employing factor XII assays, other intrinsic factor assays, factor inhibitor assays, and electroimmunoassays will be used to characterize factor XII deficiency in the cat. Cats with Hageman trait will be made available to qualified investigators desiring to establish breeding colonies.